Milling Machine, In Particular Surface Miner, And Method For Mining Milled Material Of An Open Cast Surface

ABSTRACT

In a method for milling an opencast mining surface or for milling off layers of an asphalt or concrete traffic surface with a milling machine removing the ground surface, by milling the ground surface along a predetermined milling track and by transporting the milled material via a conveying device to at least one container of a truck that travels along next to the milling machine, a relative position between the container and the conveying device is automatically controlled to regulate the loading of the container.

The invention relates to a method for milling a ground surface, as wellas to a milling machine.

In mining, earthwork and rock operations, the mining of solid earthmaterials in the form of milled material offers a great advantage overdrilling and blasting as it can be performed with much greater economicefficiency.

The milling machine, generally called a surface miner, is able to crushthe mined material to such a small size that it can be processed withoutany or requiring only minor subsequent treatment. The material removedby a milling drum is loaded, via loading conveyors, onto a truck thattravels along next to the milling machine. In the process, the milledmaterial is cut, crushed and finally loaded.

A known method provides that the ground surface of an opencast miningsurface is milled along a predetermined milling track having apredetermined length. In the process, the milling operation isoptimized, in terms of milling depth and milling speed, in accordancewith the machine's power and the type of material to be milled.

The milled material is transported via a conveying device to at leastone container of a truck that travels along next to the milling machine,said truck having a predetermined maximum loading volume per load. Oncethe truck is fully loaded, it is replaced with an unloaded truck.

At the end of the milling track, the milling machine turns so that anadjoining milling track can be removed. It is of disadvantage in thisprocess that the truck may not be fully loaded at the end of the millingtrack so that the vehicle either needs to transport the milled materialaway being only partially loaded, or else needs to wait for the turningmanoeuvre to be completed, in which case the working process will haveto be interrupted once again during the next truck change until changingof the trucks has been completed. In order to minimize the breaks inoperation, it is also known to use truck and trailer combinations thatare provided with one or several trailers. With such truck and trailercombinations, there is the problem all the more, however, of the truckand trailer combination not being fully loaded at the end of the millingtrack. As such a truck is not able to perform a turning manoeuvre, thereis the problem all the more in this arrangement of it not being possibleto fully load the truck and trailer combination.

A further problem lies in loading the container of a truck evenly inorder to be able to make maximum use of the container volume.

It is therefore the object of the present invention to specify a methodfor milling an opencast mining surface that can be performed withgreater economic efficiency.

To this end, the following is provided in accordance with the methodaccording to the present invention:

-   -   calculation of the maximum total loading volume resulting over        the length of the current milling track as a function of the        current effective working width and a milling depth that has        been optimized in relation to a predetermined, preferably        maximum milling power,    -   calculation of the number of truck loads required for the        maximum total loading volume of a milling track,    -   determination of an effective total loading volume of the        current milling track, which results from the volume of the        nearest whole number of loads, and    -   adjustment of the adjustable total milling volume of the milling        machine over the length of the milling track to match the        effective total loading volume that results in a whole number of        loads.

The invention enables the milling operation to be optimized in such amanner that, at the end of a current milling track, the container of atruck is, or containers of a truck are, also completely filled so thatjourneys of the trucks or truck and trailer combinations with containersnot fully loaded are avoided, thus also minimizing the number of breaksin operation for the purpose of changing the trucks.

At the same time, the advance speed may be increased, for example, whenworking at a reduced milling depth so that the time required for millingoff a milling track can be reduced.

It is preferably provided that the adjustable total milling volume ofthe milling machine in a milling track is adjusted to match a totalloading volume which results from the volume of the nearest lower wholenumber of loads.

In this case, adjustment of the total milling volume to match thespecified effective total loading volume is preferably effected byaltering the milling depth. The reason for this is that, by reducing themilling depth, the total milling volume within a milling track can bereduced in such a fashion that it corresponds to the specified effectivetotal loading volume that enables a whole number of loads to be achievedin a milling track.

An alternative possibility consists in adjusting the total millingvolume to match the specified effective total loading volume by alteringthe effective working width by selecting a different overlap ofadjoining milling tracks.

In this case, the milling depth optimized for the milling process ismaintained, and the reduction of the total milling volume for adjustmentto the total loading volume is adjusted by partly travelling over theprevious milling track.

It is provided in this arrangement that the advance speed of the millingmachine is adjusted to match the effective total milling volume in sucha fashion that a preselected milling power, preferably maximum millingpower, is maintained or achieved.

In order to improve the effectiveness of the milling process and theeven loading of the container, it may also be provided that the travelspeed of the truck is controlled, as a function of the advance speed ofthe milling machine, in such a fashion that the loading space of the atleast one container is loaded evenly and fully over the length up to themaximum loading volume.

This is preferably effected by regulating the loading process by meansof controlling the travel speed of the truck as a function of theadvance speed of the milling machine and of the measured loadingcondition of a container.

The travel speed or the current position of the truck may alternativelybe controlled as a function of the advance speed of the milling machine,or of the distance travelled by the milling machine in the currentmilling track, or of the current discharge position of the transportdevice.

It may further be provided that the travel speed or the current positionof the truck is controlled in such a fashion that the discharge positionof the conveying device above the at least one container moves from afront or rear end position inside the container to an end position thatis opposite in longitudinal direction.

The travel speed of the truck is preferably controlled in such a fashionthat the travel speed of the truck is higher than or equal to theadvance speed of the milling machine.

It may alternatively be provided that the travel speed of the truck iscontrolled in such a fashion that the travel speed shows a constantpositive difference to the advance speed of the milling machine.

It may alternatively be provided that the travel speed of the truck iscontrolled in such a fashion that the travel speed of the truck isaltered in a discontinuous fashion.

At the beginning of the loading process, it may be provided thatcontrolling the travel speed of the truck at a higher travel speed thanthe advance speed of the milling machine begins only after asufficiently high initial fill has been discharged at the front or rearend position.

The method can be applied to advantage in particular when truck andtrailer combinations with several trailers connected to one another inan articulated fashion are used.

In order to enable a continuous loading process, it is particularlyadvantageous in this arrangement if containers on several trailersconnected to one another in an articulated fashion are used in which theupper end edges of the opposite end walls of adjacent containersoverlap.

Containers may be used in this arrangement, the opposite end walls ofwhich are provided with a mutually adapted curvature about an axisorthogonal to the ground surface in such a fashion that the opposite endwalls have a smallest possible mutual distance but enable a mutualturning movement of the trailers both laterally and in a ramp transitionarea nonetheless.

Containers may also be used, the front end wall side of which is curvedin a convex manner and is provided, preferably at the front end edge,with a projecting collar that covers a driver's cabin of the truckand/or the rear upper concavely curved end edge of the end wall of acontainer travelling ahead.

In the following, one embodiment of the invention is explained ingreater detail with reference to the drawings.

FIG. 1 a graphic representation of a so-called opencast pit of anopencast mining surface,

FIG. 2 loading of a container of a truck via a transport conveyor of themilling machine,

FIG. 3 a side view of a surface miner,

FIG. 4 a top view of a surface miner,

FIG. 5 a complete cross-section of a pit in the working direction of themilling machine,

FIG. 6 a complete cross-section of a pit transverse to the workingdirection,

FIG. 7 definition of the actual cutting depth,

FIG. 8 material heaps with realistic and idealized loading, and

FIG. 9 a basic structure of a truck control unit.

FIG. 1 shows an opencast pit of an opencast mining surface, wherein thereference symbol 4 shows the ground surface to be processed, the area 6shows a ramp which leads to an elevated turning area 8 in the respectiveperiphery of the opencast pit. The surface miner 3 can turn in saidturning area 8 after a milling track has been removed in order toprocess an adjoining milling track in the opposite direction.

An opencast pit has a size of, for example, approx. 100 m in width andapprox. 500 m in length.

As can be seen from FIG. 2, the milled material removed by the surfaceminer 3, such as ore or coal, is loaded via a transport conveyor 2 ontoa truck 1 that may also be provided with one or several containers 10. Acontainer is located on the truck 1, said container having a loadingvolume of, for instance, 100 t. Truck and trailer combinations with atotal number of three containers of 100 t each mounted on trailers arefrequently used, so that the total loading capacity of such a truck loadamounts to approx. 300 t. When a truck with a 100-t container is used,changing of the trucks needs to be performed approx. 16 to 17 times overthe length of a milling track of approx. 500 m. This means that a shortbreak in operation during changing of the trucks is required after every30 m already, as the transport conveyor needs to be stopped and, due tothe high milling power of the milling machine, the milling process thusalso needs to be interrupted briefly during changing of the vehicles.

FIG. 2 shows a surface miner 3 that is provided with a control unit 12for controlling the removal process during the mining of milled materialof an opencast mining surface or during the milling off of layers of anasphalt or concrete traffic surface, and for controlling thetransporting away of the removed milled material for loading onto atruck.

The ground surface is removed along a predetermined milling track havinga predetermined length.

The milled material is conveyed via a conveying device, for instance, atransport conveyor 2, to at least one container of a truck 1 thattravels along next to the milling machine, said truck 1 having apredetermined maximum loading volume per load.

A fully loaded truck is replaced with an unloaded truck when the maximumloading volume of a truck load has been reached.

The control unit 12 of the milling machine 3 calculates

-   -   the maximum total loading volume resulting over the length of        the current milling track as a function of the current effective        working width and a milling depth that has been optimized in        relation to a predetermined, preferably maximum milling power,    -   the number of truck loads required for the maximum total loading        volume of a milling track, and determines    -   an effective total loading volume of the current milling track,        which results from the nearest whole number of loads.

The control unit 12 then adjusts the adjustable total milling volume ofthe milling machine over the length of the milling track to match theeffective total loading volume that results in a whole number of loads.

For the purpose of setting and adjusting the total milling volume, thecontrol unit 12 can calculate the effective total loading volume whichresults from the nearest lower whole number of loads.

For the purpose of adjusting the adjustable total milling volume tomatch the specified effective total loading volume, the control unit 12can alter, preferably reduce, the milling depth.

For the purpose of adjusting the adjustable total milling volume tomatch the specified effective total loading volume, the control unit 12can alternatively alter the effective working width by selecting adifferent overlap of adjoining milling tracks.

The control unit 12 can set the advance speed of the milling machine toa preselected milling power, preferably maximum milling power.

In addition, the control unit 12 can control the travel speed of thetruck as a function of the advance speed of the milling machine in sucha fashion that the loading space of the at least one container is loadedevenly and fully over the length up to the maximum loading volume.

The control unit 12 can regulate the loading process of at least onecontainer by controlling the travel speed of the truck as a function ofthe advance speed of the milling machine and of the measured loadingcondition of the container.

The control unit 12 can control the travel speed or the current positionof the truck as a function of the advance speed of the milling machine,or of the distance travelled by the milling machine in the currentmilling track, or of the current discharge position of the transportdevice in relation to the truck.

In this arrangement, the control unit 12 can control the travel speed orthe current position of the truck in such a fashion that the dischargeposition of the conveying device above the at least one container movesfrom a front or rear end position inside the container to an endposition that is opposite in longitudinal direction.

Preferably, the control unit can control the travel speed of the truckin such a fashion that the travel speed of the truck is higher than orequal to the advance speed of the milling machine.

The control unit 12 can increase the travel speed of the truck onlyafter a sufficiently high initial fill has been reached at the front orrear end position.

The containers may be arranged on several trailers connected to oneanother in an articulated fashion, in which case the adjacent upper endedges of the opposite end walls overlap.

The adjacent end walls of the containers on the several trailersconnected to one another in an articulated fashion may be provided witha mutually adapted curvature about an axis orthogonal to the groundsurface in such a fashion that the end walls have a smallest possiblemutual distance but enable a lateral turning movement of the trailersnonetheless.

The containers may be curved in a convex manner at the front end wallside and be provided, preferably at the front end edge, with aprojecting collar that covers a driver's cabin of the truck and/or therear upper concavely curved end edge of the end wall of a containertravelling ahead.

A dimensioning and control concept for automated opencast mining isdescribed in the following. The procedure comprises the following steps:calculation/dimensioning of the cutting depth for each layer (as afunction of a “vertical” opencast mining process, assuming that the pitdimensions are known) to achieve optimal truck loading for each layer,application of a control concept for the opencast mining/loading processto achieve optimal truck loading at minimized control and communicationefforts.

The fundamental advantage of the following control concept lies in thefact that a continuous loading process between truck and opencastmilling machine, where both machines travel at a constant speed, isespecially easy to realize with regard to the control concept andrequires almost no communication between the milling machine and thetruck (except at the beginning and at the end of the loading process).

The principle of the present invention consists in controlling the truckspeed and direction as a function of the actual position and speed ofthe milling machine (or of the position and speed of the conveyor beltof the milling machine respectively), the cutting depth and cuttingwidth of the milling machine and other process parameters known inadvance, such as the maximum payload of the truck, the equivalentloading length of the truck and the density of the milled material.

Calculation of the Optimal Cutting Depth as a Function of the VerticallyProgressing Layer Mining Process:

General Definitions and Relations:

Known Process Parameters and Variables:

-   -   l_(min e,max) in [m]: maximum total horizontal distance to be        mined without the milling machine turning back (including the        ramp and the flat part; see FIG. 5)    -   α_(ramp) in [m]: mining ramp angle; see FIG. 5    -   ρ_(mat) in [t/ m³]: density of the mined material    -   M_(pay) in [t]: payload of the truck    -   L in [−]: loosening factor, relation between the density of the        cut material and the density of the loaded material    -   F_(T,max) in [m]: maximum cutting depth    -   F_(B) in [m]: cutting width    -   F_(T,act) in [m]: actual cutting depth

Unknown process variables to be determined (in the sequence ofclarification):

-   -   l_(min e,act) in [m]: actual total horizontal distance to be        mined without the milling machine turning back (including the        ramp and the flat part; see FIG. 5)    -   L_(ramp,act) in [m]: actual horizontal distance to be mined        while the milling machine is on the ramp; see FIG. 7    -   l_(flat,act) in [m]: actual horizontal distance to be mined        while the milling machine is on the flat part of the pit        cross-section; see FIG. 7    -   Q_(ramp,act) in [m³]: material volume to be loaded on the ramp    -   Q_(flat,act) in [m³]: material volume to be loaded on the flat        part of the mining track    -   A_(total,act) in [m³]: total material volume to be loaded in a        single track    -   M_(total,act) in [t]: total weight to be loaded in a single        track    -   n_(trucks) in [−]: number of trucks required for the total load        of a single track.

FIG. 1 shows a top view of the sample of a pit, and FIGS. 5 and 6 showthe relevant cross-sections. A complete pit cross-section in the workingdirection of the milling machine is depicted in FIG. 5. In FIG. 5, 16depicts the maximum pit length, 18 depicts the maximum mining length, 21depicts the maximum mining depth, and 20 depicts the mining ramp, saidmining ramp having a slope of, for instance, 1:10˜5.71°. The completepit cross-section transverse to the working direction is depicted inFIG. 6. In FIG. 6, 22 depicts the maximum mining depth, and 24 depictsthe mining ramp, said mining ramp having a slope of, for instance,1:0.25˜76°. Let it be assumed that the total pit dimensions as well asthe cross-section are known prior to the start of the mining process.Determination of the dimensions is typically performed prior to thestart of the mining process by means of an extensive analysis ofdrilling samples.

Calculation Procedure:

-   -   Start at the top of the pit by adjusting l_(min e, act) to the        beginning of the track length and by adjusting the cutting depth        to the maximum cutting depth    -   Calculate the number of trucks required by means of the cited        procedure    -   Reduce the number of trucks required to the next smaller whole        number    -   Recalculate the cutting depth and the actual horizontal distance        on the flat part l_(flat,act)    -   Set l_(flat,act) as the starting value for l_(min e,act) to        calculate the next cutting depth

The material volume that needs to be loaded on a ramp can be calculatedfrom

$Q_{{ramp},{act}} = {\frac{1}{2} \cdot l_{{ramp},{act}} \cdot F_{T,{act}} \cdot F_{B} \cdot {L.}}$

In a similar fashion, the material volume that needs to be loaded on theflat part can be derived from

Q _(flat,act) =l _(flat,act) ·F _(T,act) ·F _(B) ·L.

The total material that needs to be loaded for the entire track issimply

Q _(total,act) =Q _(flat,act)+2·Q _(ramp,act).

Substituting the material volume of the ramp and the flat part resultsin

${Q_{{total},{act}} = {{l_{{flat},{act}} \cdot F_{T,{act}} \cdot F_{B} \cdot L} + {2 \cdot \frac{1}{2} \cdot l_{{ramp},{act}} \cdot F_{T,{act}} \cdot F_{B} \cdot L}}},$

which can be further simplified to

$Q_{{total},{act}} = {\underset{\underset{l_{{\min {\; \;}e},{act}}}{}}{\left( {l_{{flat},{act}} + l_{{{ramp},{act}}\;}} \right)} \cdot F_{T,{act}} \cdot F_{B} \cdot L}$

The total weight to be loaded is

M _(total,act) =Q _(total,act)·ρ_(mat)

The number of truck loads required for the total load is

n _(trucks) =M _(total,act) /M _(pay).

A recalculation of the required cutting depth can now be performed quiteeasily by solving the aforementioned equations for the cutting depth,which results in

$F_{T,{act}} = {\frac{Q_{{total},{act}}}{F_{B} \cdot L \cdot l_{{\min {\; \;}e},{act}}}.}$

The current total horizontal distance of the flat part can be determinedby initially calculating the distance of the ramp

$l_{{ramp},{act}} = {\frac{F_{T,{act}}}{\tan \left( \alpha_{ramp} \right)}.}$

The remaining distance of the flat part l_(flat,act) can then becalculated from (FIG. 7)

l _(flat,act) =l _(min e,act)−2·l _(ramp,act).

The total horizontal distance l_(min e, act) for calculation of the nextlayer equals the last calculated distance of the flat part

l _(min e,act) =l _(flat,act),

with the exception of the first calculation, where said length needs tobe set to the maximum initial horizontal distance l_(min e,max).

FIG. 8 shows material heaps 26 with realistic and idealized loading 28,30, with 32 depicting the loading length.

Control law for the truck speed:

General definitions and relations:

Known process parameters and variables:

F_(T) in [m]: cutting depthF_(B) in [m]: cutting widthν_(SM) in [m/min]: advance speed of the milling machineM_(pay) in [t]: payload of the truckL in [−]: loosening factor, relation between the density of the cutmaterial and the density of the loaded materialρ_(mat) in [t/m³]: density of the mined materiall_(lc) in [m]: equivalent loading length of the truck

Unknown process variables to be determined (in the sequence ofclarification):

t_(lc) in [min]: truck loading timeQ_(lc) in [m³]: material volume for one loading cycle{dot over (q)} in [m³/min]: material flow rate from the milling machineA_(tray,cr) in [m²]: loadable cross-sectional area of the truck trayν_(Truck) in [m/min]: truck speed in forward directionWhere: [min]: minutes [m]: metres [m³/min]: cubic metres per minute

The truck-loading cross-sectional area as a function of the surfacemilling machine speed, the cutting depth, the cutting width and thetruck speed can be calculated by using the following simple assumptionsand relations:

-   -   The material can be loaded onto the truck without any angle of        repose (see FIG. 8 for illustration).    -   The truck 1 and the milling machine 3 travel at a constant        speed.    -   The truck 1 starts loading at the front end of the truck tray        and travels faster than the milling machine.    -   There is no storage of material in the milling machine 3.    -   A constant loosening of the cut material takes place, i.e. the        material delivered by the conveying device equals the cut        material, multiplied by the loosening factor.

The material delivered by the milling machine 3 during a specificloading time tip can be calculated from

Q _(lc) =F _(T) ·F _(B)·ν_(SM) ·L·t _(lc) ={dot over (q)}·t _(lc).

The resulting cross-sectional loading area of the truck tray can becalculated from

A _(tray,cr) =Q _(lc) /l _(lc)

where l_(lc) represents an equivalent loading length assuming that theload deposited on the truck resembles a cuboid.

By substituting the material volume and the loading length one obtains

$\begin{matrix}{{A_{{tray},{cr}} = {F_{T} \cdot F_{B} \cdot L \cdot \frac{v_{SM}}{v_{Truck} - v_{SM}}}},} & (1)\end{matrix}$

which means that for a given cutting depth, a given cutting width and agiven loosening factor the cross-sectional loading area is a function ofthe milling machine speed and the difference of milling machine speedand truck speed. This relation can be verified quite easily. Assumingthat the truck is stationary (V_(truck)=0), it results from theaforementioned relation that

A _(tray,cr) =F _(T) ·F _(B) ·L,

which means that the material cross-section to be cut by the millingmachine, multiplied by the loosening factor, needs to be stored in thetruck 1.

To be able to obtain a particular cross-sectional loading area of thetruck tray, equation (1) produces a control law for adjusting the truckspeed and/or the milling machine speed for a given cutting depth andcutting width. In practice, the loading area is subject to a limitationthat is due to the maximum payload of the truck tray. With a givenmaximum payload of the truck tray, the maximum material volume that canbe loaded during one loading cycle is defined by

Q _(lc,max) =M _(pay)/ρ_(mat).

The maximum material volume can then be translated into a maximumcross-sectional loading area

A _(tray,cr,max) =Q _(lc,max) /l _(l/c)  (2).

Inserting (2) into (1) and solving (1) for the truck speed produces afeedforward control law for the truck speed:

$v_{Truck} = {{v_{SM}\left( {1 + \frac{F_{T} \cdot F_{B} \cdot L \cdot \rho_{mat} \cdot l_{lc}}{M_{Pay}}} \right)}.}$

The basic structure of a truck control unit is depicted in FIG. 9. Thetruck position and speed feedforward control unit 34 includes afeedforward control rule for the truck speed and for mapping theconveyor position onto the truck position. The truck position and speedfeedforward control unit 34 includes measuring values 36, such asabsolute conveyor positions and speeds, actual cutting depth and actualmilling machine speed. Additional parameters 38 exist, such as themaximum payload of the truck, the loosening factor, the materialdensity, the equivalent loading length of the truck tray, or the cuttingwidth. 40 depicts the commanded speeds and positions (direction andamplitude), 42 depicts the truck control device, 44 depicts the controlcommands, speed commands, 46 depicts the truck, 48 depicts the absolutetruck position, and 50 depicts the ATS/GPS.

What is claimed is:
 1. A method of controlling a loading process of atransport container of a transport vehicle by a milling device during amilling operation, wherein the milling device comprises a conveyor, viawhich milled material is transported to the transport container during amilling operation of the milling device, and a control unit, comprisingthe steps: a) detecting the relative position of the transport containerin a loading range of the milling device via a sensor device; b)starting the loading process by starting up the conveyor; c) monitoringthe relative position of the transport container via the sensor device;and d) issuing a signal when a predetermined fill level of the transportcontainer is determined, for stopping the loading process.
 2. A methodaccording to claim 1, wherein the control unit controls driving movementof the transport vehicle during the loading operation.
 3. A methodaccording to claim 1, wherein the control unit considers at least one ofthe following operating parameters of the milling device for controllingthe loading process: speed of the milling device during the millingoperation; milling depth of a milling rotor; and delivery speed of aconveyor belt of the conveyor.
 4. A device for controlling a loadingprocess of a transport container of a transport vehicle by a millingdevice during a milling operation, wherein the milling device comprisesa conveyor via which milled material is transported into the transportcontainer during a milling operation of the milling device, wherein thedevice comprises a sensor device designed for detection of a relativeposition of the transport container to the milling device, and in thatthe device comprises a control unit, which controls the loading processbased on the relative position of the transport container to the millingdevice detected by the sensor device.
 5. A milling machine, comprising adevice according to claim 4 for implementing a method according toclaim
 1. 6. A milling machine according to claim 5, wherein the millingmachine comprises a road milling machine or a device for removal of soilmaterial.